Oil cracking in soakers



Feb. 8, 1944. BAYNE 2,341,353

OIL CRACKING IN SOAKERS Filed Feb. 27. 1941 OAKL'R DRUM Patented Feb. 8, 1944 OIL CRACKING IN SOAKERS Charles D. Bayne, deceased, late of Baytowu Tex., by Emma T. Bayne, executrix, Baytown, Tex, assignor to Standard Oil Development Company, a corporation of Delaware Application February 27, 1941, Serial No. 386,872

4 Claims.

The present invention is directed to an improved method for cracking petroleum'oil. More particularly, it relates to a method for preventing fouling of pump-out and steam-out lines in coil and drum cracking of residual crude fractions.

In the cracking of residual crude fractions in a coil and drum cracking operation with alternating upflow drums, there is usually deposited in the soaking drum, as a result of the cracking, a mixture of coke-like hydrocarbons, tar, and heavy oily fractions. It is the practice when a coked drum is taken off of the cracking cycle to release overhead the pressure on the drum, for upfiow soakers, allowing the cracked hydro carbons to be flashed to the usual tar separator. After the pressure has been lowered to say about 100 pounds per square inch, the material remaining in the drum is then pumped out through a pump-out cooler and disposed of as seen fit. It is then customary to steam the drum for removal of volatile hydrocarbons followed by opening to remove the solid contents by conventional means such as drilling.

Prior to the present invention, difficulty has been encountered by reason of the fact that frequently the pump-out and steam-out lines and pump-out coolers have been found to be plugged by cement-like deposits which rendered them inoperative. This constituted a considerable operatin as well as life hazard since, if a pumpout and steam-out system common to two or more drums were plugged and it became necessary for any reason such as building up of excessive pressure in the operating system to suddenly release the unit to the blow-down system, plugged pump-out and steam-out lines would render pressure release therethrough impossible.

It was found on opening the drums, pump-out and steam-out lines, and pump-out coolers on cracking units where this difficulty was encountered that the material with which they were plugged was a hard cement-like mass consisting of fine petroleum coke cemented into a solid mass by solidified tarry hydrocarbons. Such deposits occur particularly in upfiow soakers which are preferably used when cracking residual crude petroleum since a greater conversion per pass is possible on this stock with upflow than with down-flow operation.

According to the present invention the dimculty of plugged pump-out and steam-out lines and associated equipment has been eliminated by depositing in the bottom of the soaking drum,

before placing it on the crackin cycle, a surficient amount of a lumpy'filter-bed material to cover the clean-outline openings. The filterbed material is preferably of irregular shape and it is important that the size of the individual lumps be larger than the diameter of the steamout and pump-out line outlet nozzle. It is also important that the material placed in the drum be of sufficient stability sothat it will not disintegrate and break down to small particles during the heat treating operation. While the lumpy material need not necessarily be of a porous nature, it is preferred to employ a porous material, such as petroleum coke, in the drum since it is believed that the-fine coke particles are filtered out of the tarry hydrocarbons during the pumpout and steam-out operation and aretherefore prevented from reaching lines and accessory equipment where plugging difficulties were encountered. Other materials such as coke derived from a coal coking process, broken stone, broken concrete, slag, natural or synthetic mineral aggregates and the like may be used.

While a bed of relatively large sized porous material satisfactorily allows pumping and steaming out of drums on a coil and drum cracking process, if complete removal of fine coke from the tarry product pumped from the drum is contemplated, it may be desirable to place a metal screen on the pump-out line outlet nozzle so that a filter bed composed of material of smaller a gregate size may be employed.

The nature of the present invention will be more clearly understood from the following detailed description of the accompanying drawing in which the figure is a front elevation in partial vertical section, of a cracking unit soaker drum embodying the present invention.

Referring to the drawing in detail: l represents a line from the heating coil of a cracking unit through which, during the cracking operation, oil heated to a temperature of from 800 to 1100 F. is introduced by branched line 2 into soaker drum 3. Numeral 4 represents a bed of lumpy, filter-bed material which was deposited in drum 3 prior to placing the latter on the cracking cycle. Cracked products are removed from drum 3 by line 5 after release of pressure through release valve 6 and are delivered to a tar separator and conventional fractionating equipment usually associated with a cracking unit.

Instead of charging the heated products into soaker 3 by lines I and 2 it may be desirable to operate with a down-flow soaker. In the latter operation, the heated oil is introduced into soaker 3 through lines 1 and 5 and cracked products are removed therefrom by means of lines 2 and 8 after release of pressure through valve 9. Preferably, however, the soaker is operated upflow.

After the cracking operation has proceeded for a length of time and operating conditions indi cate that soaker 3 has become fouled with coke, valves 9 and 6 in lines 2 and 5, respectively, are closed oil. Pressure is then gradually released from drum 3 through line 5 by release valve 6 until the pressure has been lowered from the elevated operating pressure to any suitable pressure, say 100 pounds per square inch. Valve I in blow-down line II and valve I2 in pump-out line I3 are opened and the fluid hydrocarbons are pumped out of drum 3 through pump-out cooler I4 by means of pump I5 and disposed of as desired. Valve I2 is then closed and steam is injected into soaker 3 by manipulation of valve I6 located in line H. Valve I8 in line II is opened and the soaker contents are released to a blow-down stack which is not shown. When operating in the manner described in accordance with the invention with a bed of lumpy material in soaker 3, lines II, I2 and pump-out cooler I 4 remain clear and perform the function for which they were designed.

In a typical operation in accordance with the present invention, an amount of petroleum coke suificient to maintain a level above line II is placed in soaking drum 3 prior to putting the drum into operative position in the cracking system. A crude residual petroleum charge stock is then fed into soaker 3 at a temperature between about 800" F. and 1100" F. and at a pressure in the range between about 700 and 900 pounds per square inch. After operation of the cracking unit has shown that the soaker or other running equipment has become plugged with coke, or when other considerations dictate that the soaking drum should be taken off stream, the pressure in the soaker is released and the tarry material is removed therefrom through line II as previously described.

Prior to the adoption of the present invention, plugging of the pump-out equipment was encountered of the time while operating a coil and drum cracking system on residual crudes with alternating upflow soakers. Since the adoption of the invention, plugging of the pump-out facilities has been eliminated. An appreciable monetary savings has thus resulted and an operating hazard has been obviated.

The nature and objects of the present invention having thus been described and illustrated, what is claimed as new and is desired to be secured by Letters Patent is:

1. In a process for cracking residual oils in which the oil at decomposition temperature and under high pressure is passed upwardly through an enlarged reaction zone, the improvement which consists in discontinuing the flow of oil, releasing the pressure on the residual oil to efiect the flashing off of light constituents thereof leaving a tarry residue and withdrawing the residual tarry residue from a lower point in the reaction zone after causing it to pass through a bed of an inert lumpy aggregate previously placed in the lower portion of the reaction zone whereby the tarry residue is withdrawn without danger of plugging the withdrawal lines.

2. Process in accordance with claim 1 in which the material is petroleum coke.

3. Process in accordance with claim 1 in which the material is a naturally occurring aggregate.

4. Process in accordance with claim 1 in which the material is a synthetically made aggregate.

EM'MA T. BAYNE, Executrirc of the Estate of Charles D. Bayne,

Deceased. 

